You can mod the supplied USB headset and convert them to a 3.5 mm audio jack... I've done this, takes about 15minutes. Use it to connect my HTC Touch to mu Ipod Hifi amp speakers. I can now stream my 20gb music database via upnp and wifi from my Windows Media Center machine to my HTC Touch and Ipod Hifi...
Step one: open the little microphone/answer button casing, have no fear it clicks open when you put a little screwdriver at the side where the volume wheel is. loosen the wires, and take the little board out.
Step two: de-solder the four headphone wires. the solder points are marked so easy enough for later. two ground (-) wires on the one side, two signal (+) wires on the other side. remove the headphone wires.
Step three: enter the cable from your audio jack through the whole in the casing, re-solder the wires. remember base = ground = black cable, middle = white = right signal, top = red = left signal. you only have to use one of the ground solder points because a 3.5 mm audo cable has only three cables.
Step four: test and reassemble carefully. click the cover back on.
Step five: sit back and enjoy!
Hope this helps.